Bose Gases Near Unitarity

TL;DR

This paper investigates the properties and stability of strongly interacting Bose gases near unitarity, highlighting the effects of bosonic enhancement and conditions for low three-body recombination in trapped systems.

Contribution

It reveals how bosonic enhancement shifts pair formation to the atomic side and identifies stability conditions for Bose gases near unitarity.

Findings

Pair formation is shifted to the atomic side due to bosonic enhancement.

A repulsive Bose gas remains stable until a critical scattering length $a_{s}^{\

Abstract

We study the properties of strongly interacting Bose gases at the density and temperature regime when the three-body recombination rate is substantially reduced. In this regime, one can have a Bose gas with all particles in scattering states (i.e. the "upper branch") with little loss even at unitarity over the duration of the experiment. We show that because of bosonic enhancement, pair formation is shifted to the atomic side of the original resonance (where scattering length $a_s<0$), opposite to the fermionic case. In a trap, a repulsive Bose gas remains mechanically stable when brought across resonance to the atomic side until it reaches a critical scattering length $a_{s}^{\ast}<0$. For $a_s<a_{s}^{\ast}$, the density consists of a core of upper branch bosons surrounded by an outer layer of equilibrium phase. The conditions of low three-body recombination requires that the particle number $N<\alpha (T/\omega)^{5/2}$ in a harmonic trap with frequency $\omega$, where $\alpha$ is a constant.